NITRIFICATION 413 



conversion of ammonia into nitrous acid or nitrites. 

 The former are supposed to be characteristic of Euro- 

 pean, and the latter of American soils. They are 

 sometimes referred to as nitrous ferments. 



Nitrobacter are those bacteria that convert nitrites 

 into nitrates. They are also designated nitric ferments. 

 There seem to be some differences in bacteria from 

 different soils, but the differences are slight, and the 

 conditions favoring their actions are similar. It is 

 also true that the conditions favoring the action of 

 Nitrosomonas and Nitrobacter are similar, and they 

 are generally found in the same soils, although some 

 experiments show that, in the same soil, nitrites 

 may sometimes accumulate, indicating conditions 

 more favorable to the development of the Nitrosomonas 

 bacteria. The formation of nitrates usually follows 

 closely on the production of nitrites, so that there is 

 rarely more than a trace of the latter to be found in 

 soils. A soil favorable to the process of nitrification 

 is usually well adapted to all of the processes of nitro- 

 gen transformation. 



Marked differences have been found in the nitri- 

 fying power of bacteria from different soils. Highly 

 productive soils have generally been found to contain 

 bacteria having greater nitrifying efficiency than those 

 from less productive soils, but this may not always 

 be the case, as other factors may limit the productive- 

 ness. 



281. Effect of organic matter on nitrification. 

 A peculiarity in the artificial culture of nitrifying 

 bacteria is that they cannot be grown in artificial 



